The optical network is one of the basic networks in the whole telecommunication network and it has been developed rapidly in recent years and will become the physical basis of the NGN (Next Generation Network). The optical network system mainly includes SDH (Synchronous digital hierarchy)/Sonet (Synchronous Optical Network), a wavelength optical network and etc. The conventional optical network is a system based on the central management, in which the communication between the nodes of the network is carried out in a permanent connection manner. The permanent connection manner means that the service switching relations on all the nodes are manually configured in the conventional optical network system, and such configuration generally will not be amended again in a large optical network system once it is set.
The management plane calculates the connection path of the permanent connection in advance according to the connection requirement and the usage state of the network resource, and sends cross-connection command to every node through NMI-T (network management interface for the Transport Network) along the connection path so as to perform the uniform assignment and realize the path establishment. In the initial development of the optical network, the permanent connection manner has achieved a better effect due to its simple design and low cost. However, the establishment, maintenance and release of the optical connection in the permanent connection manner need to be intervened manually or by the network manage system. With the increasing quantity of the data services, such connection manner cannot assure that the optical network system has the dynamic and flexible characteristics.
For solving the problem that the permanent connection manner can not assure that the optical network system has the dynamic and flexible characteristics in the case of the increasing quantity of the data services, ITU-T (International Telecommunication Union—Telecommunication Standardization Sector) proposes an ASON (Automatically Switched Optical Network) architecture. The ASON architecture adds a control plane in the conventional optical network, and proposes a concept of switched connection. In the ASON architecture, the optical network node firstly obtains the local adjacency relationship between itself and other adjacent optical network nodes by the discovering function of partial links, floods the state of the node itself and links via the control plane, and receives the state issuances of other nodes in the network. As a result, each optical node has a “network map” describing an accurate topology of the network. There are various kinds of information in the “network map”, such as nodes, links, resources and etc. When the user equipment or the management plane requires the node to establish the connection, the corresponding node uses the “network map” information obtained by itself to calculate a routing according to a certain routing algorithm, and uses signaling protocol to create a cross connection in all the nodes in the path so that a end-to-end connection is established.
In the ASON, each node employs the link state protocol to collect the “network map” information. The link state protocol can be only used when the network is not very large. With the expansion of the ASON, the network will be divided into a plurality of control domains. If the ASON further expands, the divided control domain will further be divided into a plurality of control domains, and eventually a multi-level ASON will be formed.
After the ASON is divided into a plurality of control domains, the procedure of establishing a connection path in a control domain is the same as that of establishing a connection path before the ASON is divided. However, when establishing one end-to-end connection path across several control domains, since each control domain is independent to each other and the nodes in each control domain do not know the “network map” information in other control domains besides that in their own domain, there is no way to calculate and establish the across-domain connection path according to the “network map” information of their own domain. Therefore, in the multi-level ASON, hierarchy routing is generally used to solve the problem of establishing an inter-domain connection path. During the procedure of establishing an inter-domain connection path by hierarchy routings, as for each high-level control domain, an adjacent control domain with a lower level is represented as an abstract node, and the links between the control domains of lower level are represented as links between the abstract nodes, and the links between the nodes in control domains of a lower level are invisible to the high-level control domain. In the high-level control domain, a similar procedure is used to realize the dissemination of link state information among the abstracts nodes, so that each abstract node in the high-level control domain can obtain the network topology information of current level, i.e. each abstract node can obtain the “network map” information of current level.
When the ASON network only has one control domain, any node has the topology information of the whole ASON network. Therefore, it is easy to determine whether another node in the network is reachable. However, in the multi-level ASON network, a node only has the outline of the whole network. The inventor finds some problems when invention on progressing as below: how to effectively determine whether another node in the network is reachable is one of main problems to be urgently solved at present. Meanwhile, on a node in the multi-level ASON network, how to effectively identify whether a link is internal link or external link also becomes a problem to be solved.
There is a method for identifying external links in the multi-level ASON network, i.e. a feeding down RC ID (routing controller identification) method. In the method, the nodes of ASON network respectively store the RC ID of the upper-layer network abstract node abstracted from the control domain to which the nodes belong. Then, the nodes obtain RC IDs, which are stored in the opposite-end node, of each layer of network abstract node through the interaction of the respectively stored RC IDs of each level of network abstract node with the opposite-end nodes. By comparing RC IDs of each layer of network abstract node stored by nodes with those of corresponding level of network abstract nodes stored in the opposite-end node, it can be determined that whether the link between a node and the opposite-end node is an external link or an internal link. Although said feeding down RC ID method enables each level of control domain in the multi-level ASON network to identify the external link among the nodes of the same level, it may not enable a node in the network to judge whether the node and other node in the network are reachable to each other. The method does not employ a concept of aggregation address, so it may not calculate the routing of a connection hierarchically.